The present invention relates to systems and methods for improved fixation of prosthetic implants within a bone. More specifically, the invention concerns the introduction of biologic material to the implantation site that can enhance the implantation and fixation of the prosthesis within the bone.
Total hip arthroplasty, or hip replacement, is rapidly becoming a prevalent orthopedic procedure as the overall population ages. For instance, at present nearly a half a million hip replacements are performed worldwide on an annual basis.
The success rate for hip arthroplasty is very high, usually greater than 90%. The hip replacement can greatly improve the quality of life for the patient by dramatically reducing the pain and disability experienced by the patient. However, as with any artificial implant, hip implants are not without problems. One common problem is that the femoral implant loosens from the femoral canal over time. Although less frequent, the acetabular cup may also loosen or dislocate over time. If the loosening is serious enough, revision surgery may be necessary to repair or replace the prosthetic implants.
Prosthetic bone and joint implants, such as the femoral prosthesis discussed above, are typically mounted in one of two ways, i.e., using cementing and non-cementing techniques. With either approach, the medullary canal of the bone is prepared by some type of boring process. In the non-cementing techniques, the prosthesis is designed to provide a tight, interference fit with the prepared medullary canal. In addition, some prostheses are anchored in place by bone screws extending into the cortical bone surrounding the prepared canal.
Cementing techniques usually require the same type of preparation of the medullary canal as non-cementing techniques. Once the canal is prepared, a restrictor plug is typically inserted into the base of the medullary canal to contain bone cement applied into the canal. The cement is usually injected into the now plugged canal and the prosthesis inserted. The prosthesis is kept stationary until the cement has cured. In the case of cementing techniques, the prosthesis is smaller than the medullary canal, leaving ample room for a layer of bone cement between the prosthesis and the bone.
Much of the recent arthroplasty development has been in improving the bone cement material itself. The most typical bone cement is composed of a polymethylmethacrylate polymer. Other developments designed to enhance the effectiveness of the bone cement have been to provide a porous coating or a mesh on the prosthesis, to utilize different cement materials, such as thermoplastic polymer, or to utilize a cement impregnated with various biocompatible materials.
While the nature of the bone cement and cementing process has been the subject of much development, little attention has been paid to preparing the implantation site itself. It is believed that non-uniformities within the prepared medullary canal can decrease the effectiveness of any cementing or non-cementing fixation technique. Certainly, the typical candidate for total hip arthroplasty is an elderly patient. One common problem faced by the elderly patient is the reduction of bone density and a commensurate increase in bone brittleness. For instance, as illustrated in FIG. 1, a patient's femur 10 having a prepared femoral canal 12 may exhibit a significant non-uniformity over much of the canal. The bone surrounding the canal may yield voids 14 or general surface irregularities 16. Likewise, the acetabulum 20, and particularly its prepared socket 22, may also exhibit similar voids 24 and irregularities 26. Not only do these voids and irregularities pose an immediate fixation problem, they can also serve as locus for further degeneration of the bone surrounding the prepared canal 12 or socket 22.
It is therefore desirable to provide some means for addressing voids and irregularities, or general weakness, in bone into which a prosthesis is engaged, whether in a cementing or a non-cementing technique.